Sandy’s Garden

Rhododendron Ponticum ... again.

Fings ain’t wot they used to be! If my memory serves, this was the title of a popular song a couple of generations ago. But Irene tells me that things are not as they used to be in Falkirk. “I came back to my home town on a visit recently,” she writes, “and cannot believe what has been done to Bantaskine Estate. There used to be lovely rhododendrons there, but I was told that they had been devastated by a contractor “improving” the area. Why destroy these lovely bushes?”

I wrote these words as the opening to a piece in 2004. And seven years later, fings are still very much wot they used to be, for the Forestry Commission Scotland (FCS) has launched a new, £15 million campaign in a bid to eradicate Rhododendron ponticum from its land over the next 15 years, because those of our Victorian ancestors who owned ‘big houses’ and their adjacent estates often imported alien species of plants to add variety to the estate landscaping. And one of these so-called exotics was a particular species of Rhododendron … Rhododendron ponticum … the Rhododendron of Pontus, which is an area of north-east Turkey. It is likely that these plants were brought to Britain from Spain and Portugal, where it also occurs naturally, and the species was very popular with Victorian estate owners, who valued it for its ornamental value and for the cover that it provided for game birds. So far so good.

However, Rhododendron ponticum bears a distinct similarity to the Trojan horse … it is rather more than it seems. Lurking in the plant’s characteristics are some qualities that are not at all desirable. It likes the British climate and, where it was planted in poor, acidic soil, it thrived, spreading by seed distribution and by the fact that, where its branches bow down and touch the ground, they develop roots which generate further branches, allowing a single parent plant to cover a substantial area of ground in time. The plant becomes extremely dense and impenetrable, a feature which stifles and suffocates other plants. And Rhododendron ponticum has a powerful defence against browsing animals … potentially toxic chemicals occur naturally in the leaves and flowers, so the plant can poison sheep or cattle that eat large quantities of it through hunger or inexperience. Yet the plant’s nectar is extremely attractive to nectar-feeding insects, which prefer the flowers of Rhododendron ponticum to those of native wild plants growing nearby, dramatically reducing the germination rate of these neighbouring plants.

It is truly a neighbour from hell so far as the natural plants of an area into which it is introduced are concerned. Almost all low-growing plants that it spreads to cover with its canopy of leaves are killed off, only the taller plants surviving. But they, too, will disappear in time, for, when large shrubs and trees succumb to age, no seedlings have survived to replace them! And, to add to Rhododendron ponticum’s nasty habits, the toxins in the leaves remain when these leaves fall from the plant and biodegrade, forming a toxic mat of humus on the ground below the plants which acts as a further barrier to any other plant life becoming established. With leathery leaves that make the plant difficult to control by spraying, grubbing the things out is usually the only option, followed by the removal of the layer of humus where the plants used to grow… and it may be many years before all the seeds in a cleared area have germinated, produced shoots and themselves been cleared. And, as if these were not sufficient problems, Rhododendron ponticum harbours tree-killing phytophthora, a large group of pathogens that cause diseases in plants, including many species of tree. All of which explains why Forestry Commission Scotland wants to eradicate Rhododendron ponticum from the 16 000 acres of its land which FCS reckons it occupies. We should all wish them luck!

Sandy Simpson, Polmont Horticultural Society